1. Field of the Invention
The present invention relates to a position measurement, i.e. position determining, system that measures the three-dimensional position of an object (including one-dimensional and two-dimensional positions) using a light emitter and an optical lens.
2. Description of Related Art
A frequently used method of measuring the three-dimensional position of a luminous object (or a high-luminance object) is as follows: a luminous object is photographed with two digital cameras and the coordinates of the luminous object are calculated with the distance between the two cameras as a base line under the principle of triangulation. However, this method requires at least two cameras and may be costly. In addition, since the focus of the camera lens must be adjusted accurately before photographing the object, only up to ten shots can be taken in one second. Also, the position of a quickly moving object cannot be measured because focusing cannot be done so quickly. Another problem is that poor focusing may result in serious deterioration in positional precision or resolution.
Another popular approach to measuring the position of a luminous object with high precision is a light interference method. One typical light interference method takes the following steps: light from a laser light source is split into two sub-beams by a beam splitter or the like; one of the sub-beams is cast on the object and the other sub-beam is reflected as reference light by a mirror and returned to the original optical path; and the reflected light from the object and the reference light are overlapped to cause interference. One advantage of this method is that it is possible to measure the position or displacement of the object at a sub-wavelength resolution. However, since it requires optical components such as a beam splitter and a reflection mirror and uses many components, it is costly. In addition, these components must be assembled with a high positioning accuracy. In short, this method is laborious and expensive. Furthermore, it also has drawbacks that an automatic focusing mechanism is needed and measurement at high speed is difficult. Another problem is that since laser beam is shaped into a spot or line before being thrown on an object, safety measures must be taken.
As a new position measurement method, a light interference lens method is proposed in the following reference:
The 63rd Autumn Meeting of the Japan Society of Applied Physics and Related Societies, Proceedings (Sep. 2002), 871 pages, 24p-ZN-7, New photometry “Light Interference Lens Method” by Yasuji Seko
In this technique, light from a semiconductor laser light source is concentrated by an optical lens to form a concentric moiré (interference) pattern on a CCD sensor and thereby measure the position of the light source. In order to form a concentric light interference moiré pattern, this technique takes advantage of the spherical aberration of a lens or uses a bifocal lens and lets light rays overlap on the CCD sensor. The light intensity of this moiré pattern sharply varies between zero and peak and the variation can be detected by an ordinary CCD sensor with high sensitivity so that the position of the light source can be measured with high resolution. In addition, the moiré pattern always appears as a clear image regardless of the distance of the light source, which makes focusing work unnecessary.
In sum, various conventional methods of measuring the three-dimensional position of a luminous object (or a high-luminance object) with high precision and high resolution have various problems: in one method, two cameras with an automatic focusing mechanism are needed, posing the problem of high cost, or high speed measurement is impossible because of required focusing time; and in another method, a laser is used and safety measures must be taken. In the light interference lens method, it is complicated work to calculate the position from a moiré pattern.